In ophthalmology, a fundus camera has generally been used to capture a picture of the fundus of the eye. In recent years, as an optical coherence tomography (hereinafter “OCT”) has appeared, capturing tomosynthesis of a retina has become possible. As a result of this, new knowledge in ophthalmology that the retina forms a layer structure and that the layer structure is destroyed as disease progresses has been discovered. At present, as disclosed in the specification of Japanese Patent Laid Open No. 2008-073099, the layer structure is extracted from the retinal volume data, which is reconstructed from plural tomosynthesis of the captured retina, and the information thereof is utilized in the diagnosis of eye disease. Hereinafter, the fundus picture and retinal volume data will be referred to the fundus image.
In the existing technology, optometrists read the image of the layer structure of the retina by using the tomosynthesis or volume data, or they read the image of the condition of a fundus blood vessel or achromoderma by using the fundus picture. The fundus blood vessel is the sole observable vessel from outside the body, and various indications or phenomena of the disease can be confirmed from the fundus blood vessel. Among them, the cross-section in which the blood vessel occupied by arterial sclerosis is enlarged and contacts the adjacent blood vessel is a known as the phenomenon that causes the blood vessel to burst and is possibly linked to blindness in the worst case. Therefore, it is meaningful for optometrists to understand the blood flow in the fundus blood vessel in order to diagnose anomalies. Further, it can be linked with early detection of the disease in patients and early recovery from or prevention of blindness. For such reasons, in the specification of Japanese Patent Laid Open No. 2007-325831, the method of extracting the two-dimensional blood vessel area from the accumulated image generated by accumulating the fundus image or luminance value in the depth direction is disclosed. Further, the method of extracting the blood vessel area or achromoderma area from the fundus picture is disclosed in Elisa Ricci, Renzo Perfetti, “Retinal Blood Vessel Segmentation Using Line Operators and Support Vector Classification, “IEEE Transactions on Medical Imaging, Vol. 26 No. 10, PP1357-1365, 2007 or Thomas Walter, Jean-Claude Klein, Pascale Messin and Ali Erginary: “A Contribution of Image Processing to the Diagnosis of Diabetic Retinopathy-Detection of Exudates in Color Fundus Image of the Human Retina, “IEEE Transactions on Medical Imaging, Vol. 21, No. 10, PP1236-PP1243, October 2002, respectively.
However, in the fundus picture, the flow in the fundus blood vessel can only be observed in two dimensions. Accordingly, three-dimensional overlap of the fundus blood vessel as seen in the cross-section cannot be observed. At present, when OCT appears and the retinal volume data can be reconstructed with high resolution from the tomosynthesis, the three-dimensional flow of the fundus blood vessel can be observed, and the cross-section can possibly be observed directly.
In order to observe the retinal volume data, a method called volume rendering in which the volume data is displayed to be translucent by converting the value owned by the voxel to opacity and color by the transfer function is effective. The transfer function governing clarity is expressed, for example, as shown in FIG. 1, as a function defining the luminance value in on horizontal axis and the opacity on the vertical axis. Generally, the user can manually set the shape of the transfer function, the position of the peak or the width of the peak using a user interface. Further, as shown in the specification of Japanese Patent Laid Open No. 2008-006274, an automatic design is possible such that the range of the CT value calculated from the average value and variance of the CT value histogram fitted by the Gaussian function is displayed to be opaque by using the fact that the CT value histogram of the internal organ or the blood vessel displayed on CT has a peak by each organ.